Flip-chip mounting of sensor chips to substrates allows for a simple and efficient manufacturing of sensor assemblies, such as e.g. described in WO 98/27411, where a sensor chip having a sensing area integrated on a first side thereof is mounted to a substrate. The sensing area is structured to measure at least one parameter of the environment, such as environmental humidity or pressure, and has therefore to be accessible. For this reason, a window of the substrate is arranged opposite to the sensing area. Contact pads integrated on the first side of the sensor chip can be used to establish electrical contacts between the sensor chip and the substrate during flip-chip mounting.
Typically, and also as shown in WO 98/27411, the gap between the sensor chip and the substrate is filled by a filler material, the so-called “underfill”. The underfill is typically applied as a liquid to one or two edges of the sensor chip after flip-chip mounting, and the liquid is then drawn into the gap using capillary forces and it is subsequently hardened.
In order to prevent the underfill from covering the sensing area, the sensor assembly of WO 98/27411 is provided with a dam extending around the sensing area and the window. Similar dams can be useful for preventing solder flux from covering the sensing area. When flip-chip mounting the sensor chip to the substrate, care must be taken to properly align the window in the substrate, the dam and the sensing area.